Because of environmental and energy consumption concerns, consumers are demanding more energy efficient products. Electronic designers are applying soft switching topologies to improve the efficiency of electronic and electrical products and to enable higher frequency operations in these products. However, switching loss has been an obstacle to power conservation, especially during high frequency operations. As such, resonant converters may be used to apply a zero-voltage switching technique to reduce switching loss occurring during turn-on or turn-off transitions of electronic devices, thereby allowing operations of higher switching frequencies than comparable converters. Resonant converters contain switching elements and resonant LC networks whose voltage or current waveforms vary sinusoidally during one or more subintervals of each switching period.
A basic switching element is an electronic component encompassing a diode and a transistor (typically a power metal-oxide-semiconductor field-effect transistor (MOSFET)) connected in parallel. In particular, a resonant converter switches the switching element when it is at the zero current or zero voltage point, which reduces the stress on the switching element and the radio interference. The zero-voltage switching (ZVS) is achieved by forcing the current flowing through the switch element to reverse its flow. When the switch current is reversed, the body diode of the switching element clamps the voltage of the switching element to a low value. This minimizes the overall energy loss within the circuitry.
Resonant converters are usually controlled by varying the switching frequency of the switching elements. Examples of the resonant converters include DC-to-high-frequency-AC inverters, resonant DC-DC converters, resonant inverters or rectifiers producing line-frequency AC, resonant AC-DC converters, resonant AC-AC converters, etc. Common applications, for instance, include personal computers, servers, telecom systems, mobile phones, automobiles, medical equipment, gaming consoles and industrial equipment, and so on.
In some instances, the switching element is turned on by a large peak current occurring during a restart process of the resonant converter. The large peak current can damage the switching element. This peak current is caused by energy remaining in a resonant network of the resonant converter after the resonant converter is turned off.